1. Field of the Invention
The present invention relates to a magnetoresistive effect element having an arrangement for obtaining a magnetoresistive effect change by causing a current to flow in the direction perpendicular to the layer surface and a magnetic memory device including this magnetoresistive effect element. Moreover, the present invention relates to a method of manufacturing this magnetoresistive effect element and a method of manufacturing this magnetic memory device.
2. Description of the Related Art
As information communication devices, in particular, personal small information communication devices such as portable terminal devices (e.g. personal digital assistants) are widely spreading, it is requested that devices such as memories and logic devices comprising these information communication devices or portable terminal devices should become higher in performance, such as they should become higher in integration degree, they can operate at higher speed and they can consume lesser electric power. Particularly, technologies that can make nonvolatile memories become higher in density and larger in storage capacity are becoming more and more important as complementary technologies for replacing hard disk devices and optical disk devices with nonvolatile memories because it is essentially difficult to miniaturize hard disk devices and optical disk devices because they have their movable portions (e.g. head seek mechanism and head rotation mechanism).
Flash memories using semiconductors, an FRAM (ferro electric random-access memory) using a ferro dielectric material and so on are known as nonvolatile memories.
However, flash memories have a defect that the information writing speed thereof is slow as the order of microseconds. On the other hand, it has been pointed out that the FRAM cannot be rewritten so many times.
A magnetic memory device called an MRAM (magnetic random-access memory) device that had been described in “Wang et al., IEEE Trans. Magn. 33 (1997), 4498”, receives a remarkable attention as a nonvolatile memory that can overcome these defects. This MRAM is simple in structure and therefore can be easily integrated at high integration degree and since the MRAM is able to record by rotation of magnetic moment, it can be rewritten a large number of times. Further, it is expected that the MRAM has very high access time and it has already been confirmed that the MRAM can be operated at speed in the order of nanoseconds.
A magnetoresistive effect element used in this MRAM and especially a ferromagnetic tunnel junction (MTJ (magnetic tunnel junction)) is essentially composed of a ferromagnetic tunnel junction formed by a laminated layer construction of a ferromagnetic material layer, a tunnel barrier layer and a ferromagnetic material layer. In this element, when an external magnetic field is applied to the ferromagnetic material layers under the condition in which a constant current flows through the ferromagnetic material layers, magnetoresistive effect appears in response to a relative angle of the magnetizations of the two ferromagnetic material layers. When the magnetization directions of the two ferromagnetic material layers are anti-parallel, a resistance value becomes the maximum. When the magnetization directions of the two ferromagnetic material layers are parallel to each other, a resistance value becomes the minimum. Functions of the memory element can be achieved when anti-parallel and parallel states of the magnetization directions are produced with application of external magnetic fields.
In particular, in a spin-valve type TMR element, one ferromagnetic material layer is coupled to an adjacent antiferromagnetic material layer in an antiferromagnetic fashion and thereby formed as a magnetization fixed layer whose magnetization direction is constantly made constant. The other ferromagnetic material layer is formed as a magnetization free layer whose magnetization direction is easily inverted with application of external magnetic fields and the like. Then, this magnetization free layer serves as an information recording layer in a magnetic memory.
For the TMR element of a spin-valve structure, a changing ratio of a resistance value in the TMR element is expressed as the following equation (A) where P1, P2 represent spin polarizabilities of the respective ferromagnetic material layers:2P1P2/(1−P1P2)  (A)
Accordingly, the changing ratio of the resistance value increases as the respective spin polarizabilities increase.
Fundamentally, the MRAM comprises a plurality of bit write lines (so-called bit lines), a plurality of word write lines (so-called word lines) and TMR elements disposed at intersection points between these bit write lines and word write lines as magnetic memory elements as disclosed in Japanese laid-open patent application No. 10-116490, for example. When information is to be written in such MRAM, information is selectively written in the TMR elements by using asteroid characteristics.
In the MRAM, when magnetic characteristics of the TMR elements fluctuate at every element or magnetic characteristics fluctuate when the same element is repeatedly used, there arises a problem in which it becomes difficult to selectively write information by using the asteroid characteristics.
Accordingly, the TMR element is requested to have magnetic characteristics that can draw an ideal asteroid curve.
To draw an ideal asteroid curve, an R-H (resistance-magnetic field) loop obtained magnetic characteristic of the TMR element are measured is free from noises such as a Barkhausen noise, a waveform should have an excellent rectangle property and the magnetization state should be stable so that a coercive force Hc hardly fluctuates.
The Barkhausen noise, the deterioration of rectangle property and the fluctuations of coercive force are caused mainly by magnetic anisotropy of the material. Since these problems arise when the direction and magnitude of the magnetic anisotropy are distributed within the layer surface, control of the direction of the magnetic anisotropy is very important.